Audio reproduction circuit

ABSTRACT

An audio reproduction circuit has an input buffer for holding MP3 data. The audio reproduction circuit also has an MP3 decoder for reading and decoding, in certain processing units, the MP3 data held in the input buffer, and generating voice data. The audio reproduction circuit also has an output buffer for holding the voice data supplied from the MP3 decoder. The audio reproduction circuit also has a digital-analog converter for reading the voice data from the output buffer in synchronization with a clock signal, and converting the voice data to an audio signal. A cut-out detector is provided for generating a cut-out detection (prediction) signal on the basis of the quantity of MP3 data remaining in the input buffer and the quantity of voice data remaining in the output buffer. The cut-out signal indicates a timing at which MP3 data is to be introduced to the input buffer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an audio reproduction circuit forreproducing voice data compressed by MP3 (MPEG audio layer 3) or anothersuch standard, and more particularly to a way of dealing with cut-outwhich could occur during voice reproduction.

2. Description of the Related Art

FIG. 2 of the accompanying drawings illustrates an example of aconventional audio reproduction circuit 10.

The audio reproduction circuit 10 is installed, for example, in a mobiletelephone or other such portable device. The audio reproduction circuit10 is connected via a system bus 2 to a CPU (central processing unit) 1that performs overall control on the mobile telephone (or other suchportable device). The audio reproduction circuit 10 decodes MP3 data DATgiven by the CPU 1, and converts the data into an audio signal AUD. TheMP3 data DAT is managed by an MP3 data file 3 connected to the CPU 1.The audio signal AUD produced by the audio reproduction circuit 10 isissued as an acoustic signal (sound) from a speaker (or speakers) 4.

The audio reproduction circuit 10 has a control register 11 for thetransfer of various kinds of control information and status informationto and from the CPU 1, and for performing management of status withinthe audio reproduction circuit 10. The audio reproduction circuit 10also has an input buffer 12 for temporarily holding MP3 data DATprovided by the CPU 1. An MP3 decoder 13 is connected to the inputbuffer 12. The input buffer 12 writes the quantity QUI of MP3 data DATremaining in the buffer to the control register 11.

The MP3 decoder 13 reads the MP3 data DAT from the input buffer 12 in576 data units called granules according to a relatively high-speedclock signal CK1, and converts the data into PCM (pulse code modulation)voice data VOI, for example. The MP3 decoder 13 writes the voice dataVOI to an output buffer 14 every time one granule of MP3 data DAT isdecoded. Upon reading the header information HDR of the MP3 data DAT,the MP3 decoder 13 writes the header information HDR to the controlregister 11.

The output buffer 14 temporarily holds the voice data VOI converted bythe MP3 decoder 13, and writes the quantity QUO of voice data VOIremaining in the output buffer to the control register 11. The outputbuffer 14 is connected to a volume adjuster 15 that reads the voice dataVOI at a specific timing and adjusts the volume according to a volumecontrol signal CON provided by the control register 11. The volumecontrol signal CON is given from the CPU 1 to the control register 11.

The volume adjuster 15 is also connected to a digital-analog converter(DAC) 16 that converts the volume-adjusted voice data VOI into theanalog audio signal AUD, and the digital-analog converter 16 isconnected to a speaker (or speakers) 4 that converts the audio signalAUD into an acoustic signal (sound). The acoustic signal is issued fromthe speaker(s) 4.

A clock signal CK2 for audio signal reproduction is provided from atiming generator 17 to the volume adjuster 15 and the digital-analogconverter 16. The timing generator 17 generates the clock signal CK2using a system clock or the like on the basis of the header informationHDR of the MP3 data held in the control register 11.

The operation of the audio reproduction circuit 10 and CPU 1 will now bedescribed.

When music or the like is generated (reproduced), the CPU 1 writes theMP3 data DAT to the input buffer 12 of the audio reproduction circuit10. Once the input buffer 12 holds one granule of the MP3 data DAT, theMP3 data DAT in the input buffer 12 is read by the MP3 decoder 13, anddecoding begins.

If header information HDR is included in the MP3 data DAT, the MP3decoder 13 writes the header information HDR to the control register 11.Once the decoding of one granule of MP3 data is complete, the MP3decoder 13 writes the resulting voice data VOI to the output buffer 14.

The timing generator 17 generates the clock signal CK2 on the basis of asampling frequency SMP stored in the control register 11, and providesthe clock signal CK2 to the volume adjuster 15 and the digital-analogconverter 16. The volume adjuster 15 sequentially reads the voice dataVOI from the output buffer 14 in synchronization with the clock signalCK2, and adjusts the volume of the voice data VOI according to thevolume control signal CON given to the control register 11. Thevolume-adjusted voice data VOI is converted into the analog audio signalAUD by the digital-analog converter 16, and is issued as an acousticsignal from the speaker(s) 4.

The CPU 1 monitors the quantity QUI of MP3 data DAT remaining in theinput buffer 12 and the quantity QUO of voice data VOI remaining in theoutput buffer 14 via the control register 11, and suitably replenishesthe data in the input buffer 12 with the next MP3 data DAT in order tocontinuously generate an acoustic signal without cut-out (or dropout oraudio discontinuity).

Such a conventional audio reproduction circuit is disclosed in, forexample, Japanese Patent Application Kokai (Laid open) publication No.2005-346838.

The following problems are encountered with the above-described audioreproduction circuit.

The CPU 1 must confirm the quantity QUI of MP3 data DAT remaining in theinput buffer 12 and the quantity QUO of voice data VOI remaining in theoutput buffer 14 via the control register 11, and replenish the data inthe input buffer 12 with the next MP3 data DAT. When there is no morevoice data VOI in the output buffer 14, and there is an obviousoccurrence of what is known as “cut-out,” in which the audioreproduction suddenly comes to a halt, a fade-out or other such volumecontrol signal CON that gradually reduces the volume must be sent fromthe CPU 1 to the control register 11.

However, in the case of a portable telephone, for example, the main jobof the CPU 1 is not audio reproduction, but speech control. Thus, it isdifficult for the CPU 1 to replenish the data and/or send a volumecontrol signal appropriately by always monitoring the remaining amountsof particular data in the input and output buffers. Consequently, thetiming of this monitoring may become delayed, thereby causing cut-out tooccur. Increasing the capacity of the input buffer 12 is one possibleway to avoid the occurrence of this cut-out, but it is often difficultto ensure adequate memory with a low-cost portable terminal. Also, sincethe processing of the MP3 decoder 13 is carried out in granule units, itis difficult for the CPU 1 to ascertain when the converted voice dataVOI is written to the output buffer 14. Thus, cut-out can suddenly occurduring audio reproduction.

SUMMARY OF THE INVENTION

It is one object of the present invention to provide an audioreproduction circuit capable of preventing sudden cut-out, without usinga large buffer memory and without placing a heavy load on the CPU 1 ofthe device.

According to one aspect of the present invention, there is provided animproved audio reproduction circuit that includes an input buffer forreceiving and temporarily holding compressed (encoded) voice data. Thisaudio reproduction circuit also includes a decoder for reading anddecoding, in certain conversion units, the voice data held in the inputbuffer, and generating decoded (uncompressed) voice data in conversionunits. The audio reproduction circuit also includes an output buffer fortemporarily holding the voice data supplied from the decoder, and adigital-analog converter for reading the voice data from the outputbuffer at a specific timing and in a sequential order, and convertingthe voice data to an audio signal. The audio reproduction circuit alsoincludes a cut-out detection unit for predicting occurrence of cut-outon the basis of a quantity of voice data remaining in the input bufferand a quantity of voice data remaining in the output buffer, andgenerating a cut-out detection signal.

The cut-out detection unit predicts the occurrence of cut-out on thebasis of a quantity of voice data remaining in the input buffer and aquantity of voice data remaining in the output buffer, and generates acut-out detection signal (or cut-out prediction signal). Therefore,there is no need for the CPU, for example, to monitor the quantity ofvoice data remaining in the input buffer and the quantity of voice dataremaining in the output buffer. Sudden cut-out can be prevented withoutusing a large buffer memory or placing a heavy load on the CPU 1 of aportable device, if the audio reproduction circuit is provided in theportable device.

The above-mentioned and other objects, aspects and advantages of thepresent invention will become evident upon reading the followingdetailed description while referring to the appended drawings. Thesedrawings, however, are given solely for illustrative purposes, and donot limit the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating the configuration of an audioreproduction circuit according to a first embodiment of the presentinvention;

FIG. 2 illustrates the configuration of a conventional audioreproduction circuit;

FIG. 3 illustrates the configuration of the cut-out detector shown inFIG. 1; and

FIG. 4 illustrates the configuration of a cut-out detector according toa second embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Embodiment 1

Referring to FIG. 1, the configuration of an audio reproduction circuit10A according to Embodiment 1 of the present invention will bedescribed. Elements of the audio reproduction circuit 10A that are thesame as or similar to those in FIG. 2 are assigned the same or similarreference numerals and symbols.

Similar to the audio reproduction circuit 10 shown in FIG. 2, the audioreproduction circuit 10A is installed, for example, in a mobiletelephone or other such portable device. This audio reproduction circuit10A is connected via a system bus 2 to a CPU 1 that performs overallcontrol of the portable device. The audio reproduction circuit 10Adecodes MP3 data DAT sent from the CPU 1, and converts the MP3 data DATinto an audio signal AUD. The MP3 data DAT is managed by an MP3 datafile 3 connected to the CPU 1, and the audio signal AUD produced by theaudio reproduction circuit 10A is sent to a speaker (or speakers) 4. Thespeaker 4 then issues sounds.

The audio reproduction circuit 10A has two additional elements (i.e., avolume controller 18 and a cut-out detector 20) as compared with theaudio reproduction circuit 10 in FIG. 2. Similar to the audioreproduction circuit 10 of FIG. 2, the audio reproduction circuit 10Ahas a control register 11 for the transfer of various kinds of controlinformation and status information to and from the CPU 1, and forperforming status management within the audio reproduction circuit 10A,and an input buffer 12 for temporarily holding MP3 data DAT provided bythe CPU 1. An MP3 decoder 13 is connected to the input buffer 12, andthe quantity QUI of MP3 data DAT remaining in the input buffer 12 iswritten to the control register 11.

The MP3 decoder 13 reads the MP3 data DAT from the input buffer 12 ingranule units according to a relatively high-speed clock signal CK1, andconverts the data into PCM encoded voice data VOI, for example. The MP3decoder 13 is connected to the output buffer 14 and writes the voicedata VOI to the output buffer 14 every time one granule of MP3 data DATis decoded. Upon reading the header information HDR of the MP3 data DAT,the MP3 decoder 13 writes the header information HDR to the controlregister 11.

The output buffer 14 temporarily holds the voice data VOI, which isprovided by the MP3 decoder 13, and writes the quantity QUO of voicedata VOI remaining in the output buffer 14 to the control register 11.The output buffer 14 is connected to a volume adjuster 15 that reads thevoice data VOI at a specific (constant) timing and adjusts the volume.

The volume adjuster 15 adjusts the volume of the voice data VOIaccording to a volume control signal CON provided by the volumecontroller 18. The volume adjuster 15 is connected to a digital-analogconverter 16 that converts the volume-adjusted voice data VOI into theanalog audio signal AUD. The digital-analog converter 16 is connected toa speaker (or speakers) 4 that converts the audio signal AUD into anacoustic signal.

A clock signal CK2 for audio signal reproduction is provided from thetiming generator 17 to the volume adjuster 15 and the digital-analogconverter 16. The timing generator 17 generates the clock signal CK2using a system clock or the like on the basis of the sampling frequencySMP held in the control register 11.

The cut-out detector 20 determines (predicts) whether or not cut-outwill occur on the basis of the remaining quantity QUI of MP3 data DATsupplied from the input buffer 12, a decoding start signal STA suppliedfrom the MP3 decoder 13, the header information HDR of the MP3 data DATsupplied also from the MP3 decoder 13, and the remaining quantity QUO ofvoice data VOI supplied from the output buffer 14. If the occurrence ofthe cut-out is predicted, the cut-out detector 20 generates a cut-outdetection signal DET. The cut-out detection signal DET is provided as aninterrupt request signal to the CPU 1. The volume controller 18 producesa volume control signal CON on the basis of a fade-out signal FAD andother signal(s) held in the control register 11 and the cut-outdetection signal DET, and controls the volume adjuster 15.

FIG. 3 illustrates the configuration of the cut-out detector 20 shown inFIG. 1.

The cut-out detector 20 has a register 21 for holding the headerinformation HDR of the MP3 data DAT given from the MP3 decoder 13. Theregister 21 holds the MPEG version number VER, the sampling rate RAT,and a channel mode MOD indicating whether the mode is stereophonic ormonophonic. The MPEG version number VER, sampling rate RAT, and channelmode MOD are all included in the header information HDR.

The MPEG version number VER and the sampling rate RAT are sent to afrequency table 22 for generating a sampling frequency FRQ. Thefrequency table 22 includes a nonvolatile ROM (read only memory) havingan address terminal and data terminal. The frequency table 22 receivesthe MPEG version number VER and sampling rate RAT at the addressterminal, and issues pre-stored data, as the sampling frequency FRQ,from the data terminal. This pre-stored data is stored in thenonvolatile ROM and retrieved as designated by the MPEG version numberVER and sampling rate RAT.

The channel mode MOD is sent to a conversion time table 23 forgenerating the decoding time per granule. The conversion time table 23has a ROM. This conversion time table 23 receives the channel mode MODat its address terminal, and issues a decoding time TMD from its dataterminal.

The cut-out detector 20 also has an input time table 24 that generatesthe time necessary for the CPU 1 to write the MP3 data DAT according tothe remaining quantity QUI of MP3 data DAT given from the input buffer12. The input time table 24 is made up of a ROM. The input time table 24receives the remaining data quantity QUI at its address terminal, andissues an input time TMI (the time necessary for the CPU 1 to write theMP3 data DAT) from its data terminal. The decoding time TMD suppliedfrom the conversion time table 23 and the input time TMI supplied fromthe input time table 24 are provided to an adder 25.

The adder 25 adds the decoding time TMD and the input time TMI toproduce the addition result SUM, which is the time until the next outputdata is obtained, after decoding one granule of data.

The cut-out detector 20 has an output time table 26 for generating theremaining output time of the output buffer 14 on the basis of theremaining quantity QUO of voice data VOI supplied from the output buffer14 and the sampling frequency FRQ supplied from the frequency table 22.The output time table 26 has a ROM. Upon receiving the samplingfrequency FRQ and the quantity QUO of voice data VOI remaining in theoutput buffer 14 at respective address terminals, the output time table26 produces the remaining output time TMO from its data terminal.

The addition result SUM given from the adder 25 and the output time TMOgiven from the output time table 26 are sent to a determination unit 27.The determination unit 27 compares the addition result SUM with theoutput time TMO when a decoding start signal STA is issued from the MP3decoder 13. The determination unit 27 generates a cut-out detectionsignal DET of “1” if the output time TMO is smaller than the additionresult SUM, and generates “0” otherwise.

The operation of the audio reproduction circuit 10A and CPU 1 will nowbe described.

When music or the like should be generated from the audio reproductioncircuit 10A, the CPU 1 reads the MP3 data DAT from the MP3 data file 3,and writes the MP3 data DAT to the input buffer 12 of the audioreproduction circuit 10A via the system bus 2. Once the input buffer 12holds one granule of the MP3 data DAT, the MP3 data DAT in the inputbuffer 12 is read by the MP3 decoder 13, and decoding begins. Thequantity QUI of the MP3 data DAT remaining in the input buffer 12 issent to the control register 11 and the cut-out detector 20.

If header information HDR is included in the MP3 data DAT, the MP3decoder 13 sends the header information HDR to the control register 11and the cut-out detector 20. Once the decoding of one granule of MP3data DAT is complete, the MP3 decoder 13 writes the voice data VOI tothe output buffer 14. At this point, the quantity QUO of voice data VOIremaining in the output buffer 14 is introduced to the control register11 and the cut-out detector 20.

The timing generator 17 produces a clock signal CK2 for audio signalreproduction on the basis of the sampling frequency SMP held in thecontrol register 11, and provides the clock signal CK2 to the volumeadjuster 15 and the digital-analog converter 16. The volume adjuster 15sequentially reads the voice data VOI from the output buffer 14 insynchronization with the clock signal CK2, and adjusts the value of thevoice data VOI according to the volume control signal CON provided bythe volume controller 18. The adjusted voice data VOI is sent to thedigital-analog converter 16 and converted into an analog audio signalAUD. This analog audio signal AUD is issued as an acoustic signal (e.g.,music) from the speaker(s) 4.

The cut-out detector 20 looks at the header information HDR of the MP3data DAT supplied from the MP3 decoder 13, and stores in its register 21the MPEG version number VER of the MP3 data DAT, the sampling rate RAT,and the channel mode MOD. The MPEG version number VER and the samplingrate RAT are converted by the frequency table 22 into the samplingfrequency FRQ, and the channel mode MOD is converted by the conversiontime table 23 into the decoding time TMD per granule.

The remaining quantity QUI of MP3 data DAT supplied from the inputbuffer 12 is converted by the input time table 24 into the input timeTMI. The input time TMI represents a time necessary for the CPU 1 towrite the MP3 data DAT. The decoding time TMD supplied from theconversion time table 23 and the input time TMI supplied from the inputtime table 24 are added by the adder 25, and the addition result SUM isprovided. The addition result SUM is the time until one granule of MP3data is decoded and the next output data (voice data) is obtained.

The remaining quantity QUO of voice data VOI supplied from the outputbuffer 14 is provided to the output time table 26 along with thesampling frequency FRQ generated from the frequency table 22, and isconverted into the remaining output time TMO of the output buffer 14.

When the decoding of the MP3 data DAT by the MP3 decoder 13 begins, thedecoding start signal STA is sent by the MP3 decoder 13 to thedetermination unit 27 of the cut-out detector 20. This causes thedetermination unit 27 to compare the addition result SUM with the outputtime TMO, and no cut-out detection signal DET is generated if the outputtime TMO is larger than the addition result SUM.

If the output time TMO is smaller than the addition result SUM, then thedetermination unit 27 generates a cut-out detection signal DET of “1.”The cut-out detection signal DET of “1” is provided as an interruptrequest signal to the CPU 1. The CPU 1 performs processing such aswriting the next MP3 data DAT to the input buffer 12, or setting(commanding) a fade-out or other such volume control signal CON in thecontrol register 11, upon receiving of the interrupt request signal.

As discussed above, the audio reproduction circuit 10A of the firstembodiment has the cut-out detector 20 for determining in advancewhether or not cut-out will occur on the basis of the header informationHDR of the MP3 data DAT, the quantity QUI of MP3 data DAT remaining inthe input buffer 12, and the quantity QUO of voice data VOI remaining inthe output buffer 14. Therefore, if the occurrence of cut-out ispredicted, a cut-out detection signal DET is generated as an interruptrequest signal to the CPU 1. Thus, the CPU 1 does not have to always orregularly read the contents of the control register 11 in order todetermine the occurrence of cut-out. This means that sudden cut-out canbe prevented without increasing the load on the CPU 1 of the main unitof the cell phone.

Embodiment 2

Referring to FIG. 4, the configuration of a cut-out detector 20Aaccording to a second embodiment of the present invention will bedescribed. The cut-out detector 20A is used in place of the cut-outdetector 20 in FIG. 1 or 3, and those elements of the cut-out detector20A that are similar to or the same as those in FIG. 3 are assignedsimilar or same reference numerals and symbols.

The cut-out detector 20A has two additional elements as compared withthe cut-out detector 20 of FIG. 3. Namely, a margin setting unit 28 anda conversion time counter 29 are added to the cut-out detector 20 inFIG. 3. Also, the cut-out detector 20A has an adder 25A and adetermination unit 27A in place of the adder 25 and determination unit27, respectively. The adder 25A has slightly different functions fromthe adder 25, and the determination unit 27A has slightly differentfunctions from the determination unit 27.

The margin setting unit 28 is a register for setting a margin MAR inorder to issue the cut-out detection signal DET with a certain margin oftime prior to actual occurrence of cut-out. This margin may be a time tobe spent for writing MP3 data DAT into the input buffer 12. In otherwords, the margin setting unit 28 adds an additional time for cut-outprevention, and the second embodiment takes a more time for cut-outprevention as compared with the first embodiment.

The conversion time counter 29 loads the decoding time TMD from theconversion time table 23 upon receiving of a decoding start signal STA,and generates a count value CNV that is reduced one at a time insynchronization with the decoding clock signal CK1. The count value CNVis a value corresponding to the remaining conversion time required toconvert the MP3 data DAT by the MP3 decoder 13.

The adder 25A adds the input time TMI given from the input time table24, the margin time MAR decided by the margin setting unit 28, and thecount value CNV of the conversion time counter 29, and generates anaddition result SUM2. The addition result SUM2 is supplied to thedetermination unit 27A.

The determination unit 27A compares the addition result SUM2 with theoutput time TMO. The determination unit 27A generates a cut-outdetection signal DET of “1” if the output time TMO is smaller than theaddition result SUM2, and generates “0” otherwise. The rest of theconfiguration of the cut-out detector 20A is the same as the cut-outdetector 20 shown in FIG. 3.

The cut-out detector 20A performs the following operation.

Upon receiving the header information HDR of the MP3 data DAT suppliedfrom the MP3 decoder 13, the register 21 holds the MPEG version numberVER of the MP3 data DAT, the sampling rate RAT, and the channel modeMOD. The MPEG version number VER and the sampling rate RAT are convertedinto the sampling frequency FRQ by the frequency table 22, and thechannel mode MOD is converted into the decoding time TMD per granule bythe conversion time table 23.

When the decoding start signal STA is given by the MP3 decoder 13, thedecoding time TMD is loaded as the initial value of the conversion timecounter 29, and thereafter the conversion time counter 29 produces acount value CNV that is reduced one at a time in synchronization withthe clock signal CK1.

The remaining quantity QUI of MP3 data DAT supplied from the inputbuffer 12 is converted by the input time table 24 to the input time TMIwhich represents a time necessary for the CPU 1 to write the MP3 dataDAT. Then, the count value CMV issued from the conversion time counter29, the input time TMI issued from the input time table 24, and themargin MAR decided by the margin setting unit 28 are added by the adder25A, and the addition result SUM2 is generated.

The remaining quantity QUO of voice data VOI supplied from the outputbuffer 14 is provided to the output time table 26 along with thesampling frequency FRQ supplied from the frequency table 22, and isconverted into the remaining output time TMO of the output buffer 14through the output time table 26.

The determination unit 27A compares the addition result SUM2 with theoutput time TMO, and produces no cut-out detection signal DET if theoutput time TMO is larger than the addition result SUM2.

If the output time TMO is smaller than the addition result SUM2, thenthe determination unit 27A generates a cut-out detection signal DET of“1.” A cut-out detection signal DET of “1” is provided as an interruptrequest signal to the CPU 1. The CPU 1 performs processing such aswriting the next MP3 data DAT to the input buffer 12, or setting afade-out or other such volume control signal CON in the control register11, upon receiving the interrupt request signal.

As discussed above, the audio reproduction circuit 20A of Embodiment 2compares the addition result SUM2, which is obtained by adding the inputtime TMI based on the quantity QUI of MP3 data DAT remaining in theinput buffer 12, the remaining conversion time (count value CNV)obtained by subtracting the time actually spent for conversion, and themargin MAR, with the output time TMO, which is based on the quantity QUOof voice data VOI remaining in the output buffer 14, and determines(predicts) occurrence of cut-out. This allows the cut-out detectionsignal DET to be generated prior to the actual occurrence of the cut-outwith the margin time MAR. Thus, the occurrence of cut-out does not haveto be determined by the CPU 1. In the prior art, the occurrence ofcut-out is determined by the CPU, and the CPU has to regularly (oralways) read and check the contents of the control register 11 to makesuch determination.

Therefore, in addition to the advantage of being able to prevent suddencut-out without increasing the load on the CPU 1, “cut-out” itself iseliminated by the circuit 20A because there is a margin for writing theMP3 data DAT to the input buffer 12.

The addition result SUM2 reflects the remaining conversion time CNVobtained by subtracting the time actually spent for conversion initiatedby the decoding start signal STA. As a result, a cut-out detectionsignal DET is generated in real time on the basis of the status of theinput buffer 12, the output buffer 14, and the MP3 decoder 13.Accordingly, possibility of cut-out can be determined accurately.

Modifications

The present invention is not limited to the above described andillustrated embodiments, and various changes and modifications can bemade within the spirit and scope of the present invention. The followingare examples of such changes and modifications.

(a) An audio reproduction circuit deals with MP3 data in the first andsecond embodiments, but the data compression and encoding format is notlimited to MP3.

(b) The volume adjuster 15 is designed to adjust the volume of thedigital voice data VOI in the first and second embodiments, but it maybe designed to adjust the volume of the analog audio signal AUD.

(c) The tables 22, 23, 24, and 26 include ROMs in the first and secondembodiments, but they may be constituted by a rewritable memory such asa RAM or EPROM. Thus, it is possible to employ a conversion table whichwill best suit for a given apparatus or equipment.

(d) Instead of the margin setting unit 28, a register may be provided inthe control register 11 that allows the margin MAR to be set from theCPU 1, for example.

(e) The margin setting unit 28 may be dispensed with from the circuitshown in FIG. 4. Without the margin setting unit 28, it is stillpossible to predict occurrence of cut-out.

This application is based on Japanese Patent Application No. 2006-222435filed on Aug. 17, 2006 and the entire disclosure thereof is incorporatedherein by reference.

1. An audio reproduction circuit comprising: an input buffer forreceiving and temporarily holding compressed voice data; a decoder forreading and decoding, in a certain conversion unit, the voice data heldin the input buffer so as to generate uncompressed voice data in theconversion unit; an output buffer for temporarily holding theuncompressed voice data supplied from the decoder; a digital-analogconverter for reading the uncompressed voice data from the output bufferat a predetermined timing in a sequential order, and converting thevoice data to an audio signal; and a cut-out detector for predictingoccurrence of cut-out on the basis of a quantity of voice data remainingin the input buffer and a quantity of voice data remaining in the outputbuffer, and generating a cut-out detection signal.
 2. The audioreproduction circuit according to claim 1, wherein the cut-out detectorincludes: a register for storing a version number, sampling rate, andchannel mode included in a header of the voice data; a frequency tablefor generating a sampling frequency on the basis of the version numberand sampling rate; a conversion time table for generating a decodingtime per the conversion unit on the basis of the channel mode; an inputtime table for generating an input time necessary to write next voicedata to the input buffer on the basis of the quantity of voice dataremaining in said input buffer; an adder for adding the decoding timesupplied from the conversion time table and the input time supplied fromthe input time table; an output time table for generating remainingoutput time of the output buffer on the basis of the quantity of voicedata remaining in said output buffer and the sampling frequency suppliedfrom the frequency table; and a determination unit for comparing anaddition result of the adder with the output time supplied from theoutput time table at a timing at which the decoder begins decoding inthe conversion unit, and generating the cut-out detection signal if saidoutput time is shorter than said addition result.
 3. The audioreproduction circuit according to claim 1, wherein the cut-out detectorincludes: a register for storing a version number, sampling rate, andchannel mode included in a header of the voice data; a frequency tablefor generating a sampling frequency on the basis of the version numberand sampling rate; a conversion time table for generating a decodingtime per the conversion unit on the basis of the channel mode; aconversion time counter for receiving as an initial value the decodingtime supplied from the conversion time table at a timing at which thedecoder begins decoding in the conversion unit, and subtracting timeactually spent for processing of said decoder from the initial value tocalculate a remaining processing time of said decoder; an input timetable for generating an input time necessary to write next voice data tothe input buffer on the basis of the quantity of voice data remaining insaid input buffer; a margin setting unit for setting margin whichenables generation of the cut-out detection signal prior to actualoccurrence of the cut-out; an adder for adding the remaining processingtime supplied from the conversion time counter, the input time suppliedfrom the input time table, and the margin supplied from the marginsetting unit; an output time table for generating the remaining outputtime of the output buffer on the basis of the quantity of voice dataremaining in said output buffer and the sampling frequency supplied fromthe frequency table; and a determination unit for comparing an additionresult of the adder with the output time supplied from the output timetable, and generating the cut-out detection signal if said output timeis shorter than the addition result.
 4. The audio reproduction circuitaccording to claim 1, wherein the cut-out detection signal is aninterrupt signal, and the interrupt signal is supplied to a source ofthe compressed voice data.
 5. The audio reproduction circuit accordingto claim 1 further comprising a volume adjuster for adjusting a volumeof the audio signal on the basis of the cut-out detection signal.
 6. Theaudio reproduction circuit according to claim 2, wherein the channelmode indicates whether the voice data is stereophonic or monophonic. 7.The audio reproduction circuit according to claim 3, wherein the channelmode indicates whether the voice data is stereophonic or monophonic. 8.The audio reproduction circuit according to claim 1, wherein the cut-outdetector includes: a register for storing a version number, samplingrate, and channel mode included in a header of the voice data; afrequency table for generating a sampling frequency on the basis of theversion number and sampling rate; a conversion time table for generatinga decoding time per the conversion unit on the basis of the channelmode; a conversion time counter for receiving as an initial value thedecoding time supplied from the conversion time table at a timing atwhich the decoder begins decoding in the conversion units, andsubtracting time actually spent for processing of said decoder from theinitial value to calculate a remaining processing time of said decoder;an input time table for generating an input time necessary to write nextvoice data to the input buffer on the basis of the quantity of voicedata remaining in said input buffer; an adder for adding the remainingprocessing time supplied from the conversion time counter and the inputtime supplied from the input time table; an output time table forgenerating the remaining output time of the output buffer on the basisof the quantity of voice data remaining in said output buffer and thesampling frequency supplied from the frequency table; and adetermination unit for comparing an addition result of the adder withthe output time supplied from the output time table, and generating thecut-out detection signal if said output time is shorter than theaddition result.
 9. The audio reproduction circuit according to claim 8further comprising a margin setting unit for setting an additional time,and wherein the adder adds the remaining processing time, the input timeand the margin.
 10. An audio reproduction circuit comprising: an inputbuffer for receiving and temporarily holding compressed voice data; adecoder for reading and decoding, in a certain conversion unit, thevoice data held in the input buffer so as to generate uncompressed voicedata in the conversion unit; an output buffer for temporarily holdingthe uncompressed voice data supplied from the decoder; and a cut-outdetector for predicting occurrence of cut-out on the basis of a quantityof voice data remaining in the input buffer and a quantity of voice dataremaining in the output buffer, and generating a cut-out detectionsignal.
 11. The audio reproduction circuit according to claim 10,wherein the cut-out detector includes: a register for storing a versionnumber, sampling rate, and channel mode included in the voice data; afrequency table for generating a sampling frequency on the basis of theversion number and sampling rate; a conversion time table for generatinga decoding time per the conversion unit on the basis of the channelmode; an input time table for generating an input time necessary towrite next voice data to the input buffer on the basis of the quantityof voice data remaining in said input buffer; an adder for adding thedecoding time and the input time; an output time table for generatingremaining output time of the output buffer on the basis of the quantityof voice data remaining in said output buffer and the sampling frequencysupplied from the frequency table; and a determination unit forcomparing an addition result of the adder with the output time at atiming at which the decoder begins decoding in the conversion unit, andgenerating the cut-out detection signal if said output time is shorterthan said addition result.
 12. The audio reproduction circuit accordingto claim 10, wherein the cut-out detector includes: a register forstoring a version number, sampling rate, and channel mode included inthe voice data; a frequency table for generating a sampling frequency onthe basis of the version number and sampling rate; a conversion timetable for generating a decoding time per the conversion unit on thebasis of the channel mode; a conversion time counter for receiving as aninitial value the decoding time at a timing at which the decoder beginsdecoding in the conversion unit, and subtracting time actually spent forprocessing of said decoder from the initial value to calculate aremaining processing time of said decoder; an input time table forgenerating an input time necessary to write next voice data to the inputbuffer on the basis of the quantity of voice data remaining in saidinput buffer; an adder for adding the remaining processing time and theinput time; an output time table for generating the remaining outputtime of the output buffer on the basis of the quantity of voice dataremaining in said output buffer and the sampling frequency; and adetermination unit for comparing an addition result of the adder withthe output time, and generating the cut-out detection signal if saidoutput time is shorter than the addition result.
 13. The audioreproduction circuit according to claim 10, wherein the cut-outdetection signal is an interrupt signal, and the interrupt signal issupplied to a source of the compressed voice data.
 14. The audioreproduction circuit according to claim 10 further comprising: adigital-analog converter for reading the uncompressed voice data fromthe output buffer at a predetermined timing in a sequential order, andconverting the voice data to an audio signal; and a volume adjuster foradjusting a volume of the audio signal on the basis of the cut-outdetection signal.
 15. The audio reproduction circuit according to claim11, wherein the channel mode indicates whether the voice data isstereophonic or monophonic.
 16. The audio reproduction circuit accordingto claim 12, wherein the channel mode indicates whether the voice datais stereophonic or monophonic.
 17. The audio reproduction circuitaccording to claim 12 further comprising a margin setting unit forsetting margin, and wherein the adder adds the remaining processingtime, the input time and the margin.